Upon my recent travel to four different airport, I had the chance of trying out wifi offered at three different airport, or at least, attempted to.
First airport – Portland International Airport. Which offers free wifi, covers most of the airport gates and lobbies. When you first turn on your computer, you will see this:

Second airport – Orlando International Airport. Wifi? What wifi, they simply don’t offer it.
Third airport – Salt Lake City. It is a bigger airport than PDX, and they do offer wifi. But this is what I find funny. They have whole bunch of flyers, posters, telling people how great the airport is, they offer wifi! Yet it’s just the same thing as Starbucks “hotspot” wifi service, where you have to pay something like $10 for 24 hours.
Verdict: PDX wins all. Free wifi everywhere!
UPDATE:
Upon Mizuki’s question of what other airport offers free wifi, I also found a list of free wifi offered in oregon. [Link]
Is there any other airport that offers WiFi for free?
PDX is the only one I know so far…
Micchan, here is for your information
http://www.wififreespot.com/airport.html